Vector completion mask handling

Title: Vector completion mask handling.Abstract: Techniques for vector completion mask (VCM) handling are provided. A data structure includes a mask field for each operand of a particular operation. A processor attempts to execute the operation with multiple operands, which are identified in the data structure by the mask fields. If operands are successfully retrieved for execution with the operation, then the corresponding mask field within the data structure is cleared. The processor can reset if any field remains set within the data structure and can re-process the operation with operands that were not previously handled with the operation. ...

BACKGROUND

Vector computing is a technique that entails executing a single operation while operating on collections of multiple elements or elements in arrays, or “vectors”, with that single operation. A vector may be characterized as a list of elements (or “operands”) processed by an operation. So, a single operation can be executed once with multiple operands, within machine architectures designed to perform vector computing. For example, if 6 numbers were to be repetitively added together within a program via a loop programming construct; then, rather than executing the addition operation multiple times, a vector processor could arrange to process a single addition operation at execution on all 6 numbers at once. This provides processor efficiency and increases operational throughput.

The benefits of vector processing include: 1) a reduced number of instructions needed to perform an operation on multiple operands; 2) each vector instruction may indicate operand dependency to processing logic, which the processing logic may exploit to increase processing performance; and 3) vector processing enables greater parallel processing of data.

A “mask” vector having the same number of elements as a vector instruction's operands, can be used to specify which of the elements of the vector operands should be operated on. This is especially beneficial when performing applications code with conditional statements using vector computing.

One challenge with vector processing is in the area of memory operations, such as vector loads addressing virtual paged memory. In this case one or more of the operands may not be available in memory for the processor to handle at the time the operation is executed. With such a situation, the processor flushes its contents (restarts) and attempts to acquire the missing operand and then attempts to process the operation again.

In virtual paged memory systems, the actual physical memory in the system may be over-subscribed and pages that do not fit in the physical memory system may be stored elsewhere, such as on a hard-drive. When a page is needed that is not currently in the physical memory, it may need to be acquired from the hard-drive, for example, which can adversely affect processing performance.

Since the element in a vector can be read from multiple locations in memory, a common situation may entail several restarts before an operation is successfully processed. This happens when elements that are loaded into a vector are located in different physical pages that need to be acquired. However, during each restart the processor is not making any forward progress on the operation. That is, no results or running results are available until the operation successfully processes with all the operands at once. Further, the process of acquiring additional elements may displace the first elements acquired. Hence, we need a system of incrementally completing the operation, so that forward progress and efficient processing is guaranteed.

The current invention allows a novel and efficient handling of the progress that is done for each attempt to execute a vector operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a processor to perform at least one embodiment of the invention.

FIG. 2 is a diagram of a method to handle and to manage the completion of vector operations, according to an example embodiment.

FIG. 3 is a diagram of another method to handle and to manage the completion of vector operations, according to an example embodiment.

FIG. 4 is a diagram of vector completion mask handling apparatus, according to an example embodiment.

FIG. 5 is a diagram of a vector completion mask handling system, according to an example embodiment.

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a block diagram of an example vector processor, in which one embodiment may be used. In one embodiment, the processor includes front end 100 that fetches and decodes instructions, an allocation unit 101 that allocates processor resources to execute the instructions, execution units 105 that include the functional units for memory operations and non-memory operations, in one embodiment, a retirement unit 110 that checks that instructions are correctly performed and that the result can be commit to architectural state. In one embodiment, vector processor may include registers, such as a VM (vector mask) storage register 115 and a VCM (Vector Completion Mask) storage register 117.

In one embodiment, the VM and VCM registers specify which of the elements of a vector should be operated upon. In one embodiment, VM and VCM registers may store Boolean vector values of the same length as the operand vector values. In one embodiment, bits set in a position in the vectors indicate that that the corresponding operand should be operated upon and other operands should not.

In one embodiment, VM register bits are set by vector conditional operations, whereas VCM register bits are set by the retirement block as will be described. In order to maintain the correct state of the VCM register, other instructions may read and write the VCM register as appropriate.

In one embodiment, VM and VCM registers are programmed with the appropriate mask and data values according to an instruction being allocated within the processor. In other embodiments, VM and VCM registers may be programmed with the appropriate mask and data values when the corresponding instruction is at other stages in the processor pipeline. The combined VM/VCM mask follow the operands through the execution units so that only operations and updates that are for elements with a corresponding TRUE value in the mack are performed.

In one embodiment, in which the VCM register indicates Boolean values, only instruction operands corresponding to a “true” value in the corresponding VCM mask may be operated upon. In one embodiment, instruction operands that have already been operated upon by an instruction may be so indicated by a “false” value in the corresponding VCM register element.

A “false” value in the corresponding VCM register element may cause a delay in processing or result in incorrect processor behavior, in which case, the mask value stored in the VCM contents may be sent to the memory system. In one embodiment, only operands that have yet to be operated upon will be loaded from memory and processed. In one embodiment, when the retirement unit receives completed data from the execution unit, and updates the corresponding element of the VCM mask for this operation, by setting it to a “false” value.

In one embodiment, if an operand cannot be operated on (e.g., the operand is not available in physical memory), a failure to complete operation will be signaled to the retirement unit. In one embodiment, when the retirement units received a failure signal, it will save architectural state (e.g. register values, program counter value, failing instructions, VCM vector values, etc.). Then the processor may be flushed of all current operations and restarted, such that a routine will be performed to acquire the missing operands from memory.

When the missing operands have been acquired, the processor may be restarted in the saved state. The VCM vector may then be updated such that processing will start with exactly the operand that was failing.

In one embodiment, the VCM register for an operation can be renamed to allow multiple instructions to be executing concurrently. Therefore, the retirement unit may update the appropriate renamed VCM register for the instructions using the VCM register. If a failure occurs, the appropriate renamed VCM register may be saved to memory and later used to restart the processor in the appropriate state.

FIG. 2 is a diagram of a method 200 to handle and to manage the completion of vector operations, according to an example embodiment. The method 200 (hereinafter “vector completion mask (VCM) service”) is implemented within a machine-accessible medium and operational within a machine. Optionally, the VCM service processes over a network that may be wired, wireless, or a combination of wired and wireless. According to an embodiment, the VCM service is integrated as a sub service or feature within a vector processor hardware or vector processor\'s instruction set or firmware. So, existing vector architectures may be enhanced to perform the processing of the VCM service.

Initially, at 210, the VCM service associates multiple operands for a single operation within a processor. That is, the VCM service identifies addresses or identifiers for obtaining operands associated with an operation that the processor is executing or is about to execute within a machine or device.

According to an embodiment, at 211, the VCM service initializes a string of bits associated with a data structure by setting each bit of that data structure to a logical “1” value (turning the bits on or setting them). The identity of that data structure is obtained and is acquired for evaluation, at 212, in response to an identifier associated with the operation, which the processor is executing or is about to execute within the machine or device.

The data structure may be viewed as a bit mask or array, such that each operation supported by the processor\'s instruction set, or some configurable subset thereof, includes its own unique data structure or bit mask. Each mask, field, or bit within the data structure refers to a specific one of the operands of the operation that the processor is executing or is about to execute.

The data structure presented is demonstrated more completely herein and below. Essentially the data structure serves as a mechanism or conduit from which the processor may continue to make forward progress on an operation that is being executed in a vector computing environment with multiple operands, when the operands are available or at least some of those operands are available to the processor during different cycles of the processor. Of course forward progress assumes that during each iteration at least one new operand that was previously unavailable becomes available.

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20121025|20120272046|vector completion mask handling|Techniques for vector completion mask (VCM) handling are provided. A data structure includes a mask field for each operand of a particular operation. A processor attempts to execute the operation with multiple operands, which are identified in the data structure by the mask fields. If operands are successfully retrieved for |